Process of purifying 1,1,1,3,3,-pentafluoro-2,3 dichloropropane

ABSTRACT

A mixture containing hydrogen fluoride and 1,1,1,3,3-pentafluoro-2,3-dichloropropane is subjected to distillation to form an azeotropic composition of 85 to 95 mol % of hydrogen fluoride and 15 to 5 mol % of 1,1,1,3,3-pentafluoro-2,3-dichloropropane, and the azeotropic composition is liquid-separated to form a lower liquid phase. Then, an azeotropic composition is withdrawn from the lower liquid phase by distillation, whereby 1,1,1,3,3-pentafluoro-2,3-dichloropropane is obtained. 
     Without formation of an aqueous solution of diluted hydrofluoric acid, 1,1,1,3,3-pentafluoro-2,3-dichloropropane is obtained which is substantially free of hydrogen fluoride.

TECHNICAL FIELD

The present invention relates to a process of concentrating or purifying1,1,1,3,3-pentafluoro-2,3-dichloropropane (hereinafter, referred to asR-225da) by separating hydrogen fluoride (hereinafter, referred to asHF) from a mixture which mainly contains HF and R-225da, and a processof concentrating or purifying HF by separating R-225da from such amixture.

BACKGROUND ART

R-225da is usually produced by reacting a chlorinated hydrocarbon suchas hexachloropropene with HF under the presence of for example antimonyhalide as catalyst. As a separation manner of R-225da from a reactionmixture from the reaction step, a process is employed in which thereaction mixture is subjected to simple distillation so that thecatalyst is removed and a resulted mixture comprising HF and R-225da iswashed with water so as to isolate R-225da. However, such a separationmanner forms a large amount of an aqueous solution of dilutedhydrofluoric acid, and an apparatus is therefore required which treatsthe solution. Further, a large amount of an alkali is required whichneutralizes the solution. Thus, the above described separation manner isnot necessarily effective.

DISCLOSURE OF INVENTION

The present inventors have made extensive studies on a process whichseparates HF from a mixture comprising HF (of which boiling point is 20°C. at 1 atm.) and R-225da (of which boiling point is 50.4° C. at 1 atm.)as main components, and found that HF and R-225da form a minimumazeotropic composition having a molar ratio of about 90/10 (its boilingpoint is 18° C. under a pressure of 1 Kg/cm² -abs).

It has been further found that such an azeotropic composition isseparated into an upper liquid phase (liquid layer) which is rich in HFand a lower liquid phase which is rich in R-225da (liquid layer)(namely, liquid separation) at a temperature which is generally used inindustries, for example in a range of 80° to -60° C., which haveresulted in the present invention.

Especially, the present invention provides an azeotropic composition (oran azeotropic mixture) which consists substantially of HF and R-225da,and in particular an azeotropic composition which contains 85 to 95 mol% of HF and 15 to 5 mol % of R-225da (boiling point in a range of 18° to50° C.) under a pressure in a range of 1 to 5 Kg/cm² (abs).

In addition, the present invention provides a process of separating HFor R-225da from a mixture which comprises HF and R-225da characterizedin that the mixture is subjected to distillation using the formation ofthe azeotropic composition so that HF and R-225da is distilled off asthe azeotropic composition, and the balance are obtained as a bottomproduct. The balance is rich in one of the components, and preferablyconsists substantially of one component.

That is, the present invention provides a process of concentrating (orpurifying) R-225da or HF by separating HF or R-225da from a mixturecomprising HF and R-225da as a feed in which process the mixture issubjected to an azeotropic distillation step so as to distill off anazeotropic composition from an enriching zone of the distillation step,for example from a top of a distillation column, and obtain, from arecovery zone of the distillation step, for example a bottom of thedistillation column, R-225da of which HF content is reduced relative tothat of the feed and which is preferably substantially free of HF, or HFof which R-225da content is reduced relative to that of the feed andwhich is preferably substantially free of R-225da, depending on acomposition of the mixture.

Further, the present invention provides a process of concentratingR-225da by separating HF which process is characterized in that anazeotropic mixture resulted from azeotropic distillation which consistssubstantially of HF and R-225da is phase separated into an upper liquidphase which is rich in HF and a lower liquid phase which is rich inR-225da, and the lower liquid phase is supplied to another distillationcolumn so that an azeotropic composition is again distilled off from itstop and R-225da which does not substantially contain HF is obtained fromits bottom. The present invention also provides a process forconcentrating HF by separating R-225da in which process a separatedupper liquid phase is subjected to azeotropic distillation so as todistill off an azeotropic composition from a column top and HF which issubstantially free from R-225da is obtained from a column bottom.

In the context of the present specification, "depending on a compositionof the mixture"is intended to mean that which of HF and R-225da isobtained from the recovery zone is necessarily determined based on aresult when HF and R-225da compositions of the mixture as the feed arecompared with the those compositions of the azeotropic mixture.

That is, it means that when an amount of HF contained in the feed isless than an amount which is required for the formation of theazeotropic composition with R-225da contained in the feed, a mixture isobtained from the recovery zone of the distillation step such as acolumn bottom of which HF content is smaller than an HF content of thefeed and of which main component is R-225da, and preferably R-225dawhich is substantially free of HF is obtained from the recovery zone. Italso means that to the contrary when an amount of HF contained in thefeed is larger than an amount which is required for the formation of theazeotropic composition with R-225da contained in the feed, a mixture isobtained from the recovery zone of the distillation step such as acolumn bottom of which R-225da content is smaller than an R-225dacontent of the feed and of which main component is HF, and preferably HFwhich is substantially free of R-225da is obtained from the recoveryzone.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a vapor-liquid equilibrium of a binary systemof HF-R-225da.

FIG. 2 is a graph showing a mutual solubility (a liquid-liquidequilibrium) of a binary system of HF-R-225da.

DETAILED DESCRIPTION OF INVENTION

According to the present invention, the distillation of the mixtureconsisting substantially of HF and R-225da distills off the azeotropicmixture of R-225da and HF from the column top, and the mixture as abottom product is obtained from the column bottom. A content of eitherone component of the mixture is substantially increased relative to acontent of that component in the feed (thus, a content of the othercomponent is substantially reduced), and preferably the mixture hardlycontains the other component.

The mixture of HF and R-225da which is supplied to the azeotropicdistillation as the feed may have any composition. Usually, the contentof R-225da of the mixture is not more than 10 mol %, and preferably notmore than 5 mol %.

The mixture as the feed may be of two separated liquid phase condition,in which case it may be supplied to the distillation step as it is orafter mixing using any suitable means so as to homogenize, or only theupper phase or the lower phase may be supplied to the distillation step.Alternatively, each phase may be supplied to a different distillationstep.

It is noted that the distilled azeotropic composition isliquid-separated into the upper phase which is rich in HF and the lowerphase which is rich in R-225da, and these two phases may be againsupplied to the distillation steps; namely, the lower phase which isrich in R-225da is subjected to the distillation so as to distill offthe azeotropic composition of HF and R-225da, whereby R-225da which issubstantially free of HF may be obtained as a bottom product, and theupper phase may be similarly distilled so as to obtain HF which issubstantially free of R-225da as a bottom product.

Accordingly, in one preferable embodiment of the present invention, amixture which contains HF and R-225da is subjected to the distillationso that an azeotropic composition is distilled off which contains 85 to95 mol % of HF and 15 to 5 mol % of R-225da; the azeotropic compositionis liquid separated so that the lower phase which is rich in HF and theupper phase which is rich in R-225da are formed; and then the lowerliquid phase is subjected to a distillation step again so as to removethe azeotropic composition of HF and R-225da from the lower phase,whereby R-225da which is substantially free of HF is obtained as abottom product.

In the present invention, the mixture as the feed may contain, inaddition to HF and R-225da, an additional component(s) unless itsubstantially provides the azeotropic phenomenon with an adverse effect.For example, the mixture may contain a material of which boiling pointis higher than those of HF and R-225da (for example, catalyst which isrequired for the production of R-225da), or the mixture may be areaction product which contains unreacted raw material(s) which isrequired for the production of R-225da. The catalyst is, for example,antimony halide. As the reaction raw materials, hexachloropropene and3,3,3-trifluoro-1,2,2-trichloropropene can be exemplified. Such areaction product contains, for example, 94 mol % of HF and 5 mol % ofR-225da, and it contains, in addition to those, 0.5 mol % of theantimony halide and 0.5 mol % of 3,3,3-trifluoro-1,2,2-trichloropropene.

As to a temperature at which the azeotropic composition is subjected tothe liquid separation, a lower temperature is better since the lowertemperature leads to an increased ratio of R-225da contained in thelower phase and an increased ratio of HF contained in the upper phase.Since the azeotropic composition according to the present invention isliquid-separated in a wide temperature range, the liquid separation canbe carried out at any temperature provided that such a temperature isindustrially possible. Thus, the liquid-separation temperature is notlimited. However, the liquid separation temperature is preferably in arange of 80° to -60° C., and more preferably in a range of 40 to -40 °C. Considering energy which is required for cooling, the liquidseparation is most preferably carried out at a temperature in a range of20° to -20° C. The liquid separation can be easily carried out bysettling in a normal vessel the mixture which is to be separated.Coalescer may be provided in the vessel so as to promote the liquidseparation.

In the present invention, HF and R-225da form the azeotropic compositionat any pressure if it is an industrially applicable pressure. Forexample, an azeotropic composition (85 mol % of HF and 15 mol % ofR-225da, boiling point of 42° C. at a pressure of 3.1 Kg/cm² -abs) andan azeotropic composition (87 mol % of HF and 13 mol % of R-225da,boiling point of 18 ° C at a pressure of 1 Kg/cm² -abs) are formed.

A distillation apparatus which is used for the azeotropic distillationaccording to the present invention may be any apparatus which hasfunctions necessary for the distillation. A simple distillationapparatus or a fractionation apparatus having trays or packing may beused. The latter is in particular preferable. The distillation may becarried out batch-wise or continuously.

For example, the concentrated or purified hydrogen fluoride obtained bythe distillation may be re-used for the reaction for the production ofR-225da. The azeotropic composition of HF and R-225da can be used as areflux stream which is returned to the distillation step as it is, or itcan be used for the next distillation after the liquid separationthereof. R-225da obtained from the column bottom of the distillationstep can be used as it is as a final product or it may be subjected toan additional treatment, for example a distillation so as to remove atrace amount of impurities.

EXAMPLES

The present invention will be explained hereinafter with reference toExamples:

Example 1

A vapor-liquid equilibrium of R-225da and HF was measured at atemperature of 40° C. under a pressure of 3.1 atm (abs). Upon themeasurement of the vapor-liquid equilibrium, R-225da and HF were mixedat a predetermined ratio and kept them at 40° C., of which vapor phasewas analyzed. A gas chromatography (GLC) equipped with a TCD detectorwas used for the purpose of R-225da measurement, and an F-ion meter wasused for the purpose of F ion concentration measurement afterneutralization of HF. The measurement results are shown in FIG. 1.

It has been found based on FIG. 1 that HF and R-225da form theazeotropic composition (a ratio of HF:R-225da was about 9 mol:1 mol).The boiling point was 42° C. Thus, it has been confirmed that HF (ofwhich boiling point is 65° C. at 3.1 atm) and R-225da (of which boilingpoint is 110° C. at 3.1 atm) form the minimum azeotropic composition.

Similarly to the above, other vapor-liquid equilibriums were alsomeasured under different pressures, the results thereof are as thosedescribed in the above with respect to the azeotropic composition.

Example 2

A mutual solubility between HF and R-225da was measured. For thismeasurement, a manner was employed in which R-225da and HF mixed in apredetermined ratio were gradually cooled and a temperature was detectedat which the mixture was separated into two phases.

The measurement results are shown in FIG. 2 in which mol % of HF isplotted along the abscissa axis and temperature is plotted along theordinate axis. Liquid of which composition is within the center regionof three regions in the graph which are divided by the solid linescannot be substantially present as a single homogeneous phase liquid andsuch liquid is phase-separated into homogeneous liquid of whichcomposition is within the right side region and homogeneous liquid ofwhich composition is within the left side region.

Since an HF concentration in the azeotropic composition of HF andR-225da is about 10 to 15 mol %, it is seen from FIG. 2 that theazeotropic composition is separated into two liquid phases at anyindustrially possible temperature, for example in a range of 80° to -60°C., and preferably in a range of 40° to -40° C.

Example 3

After sufficiently degassing a stainless steel made distillationapparatus (packing height: 50 cm, theoretical plate number: 20 stages,column diameter: 25 mm), a mixture of 800 g of HF (40 mol) and 200 g ofR-225da (1 mol) was charged into a bottom (still pot) of the column, andthe apparatus was operated at a total reflux condition (operatingpressure: 3.1 Kg/cm² -abs). When gas from the column top was analyzed, aratio of HF:R-225da in the gas was found about 9 mol:1 mol (column toptemperature was 42° C.). While operating at the total reflux condition,distillates were intermittently removed from the distillation system tothe outside. During the intermittent removal, the ratio of HF to R-225daof the distillate was substantially not changed until almost all R-225dawas distilled off from the apparatus. A content of R-225da in theobtained bottom product was 13 mol %.

In this way, 357 g of the azeotropic composition was obtained. Theazeotropic composition was separated into two phases at a temperature of30° C. The composition was further cooled to 0° C., and then the lowerliquid phase which was rich in R-225da was withdrawn to obtain a mixture(145 g) of HF and R-225da (HF: 5 mol).

This lower phase was again distilled. 3 Grams of the azeotropiccomposition was distilled off from the column top and 141 g of R-225dawhich did not substantially contain HF (HF content is not more than 0.05mol %) was obtained from the column bottom.

Example 4

Operating similarly to Example 3, 357 g of the distilled azeotropiccomposition was obtained. The azeotropic composition was liquidseparated while keeping it at a temperature of 20° C., and then thelower phase which was rich in R-225da was withdrawn to obtain 129 g of amixture of R-225da and HF (HF content: 7.5 %).

The lower phase was again distilled and 5 g of the azeotropiccomposition was removed as the first distillate and 123 g of R-255da wasobtained which did not substantially contain HF.

We claim:
 1. An azeotropic composition consisting of 85 to 95 mol% ofhydrogen fluoride and 15 to 5 mol% of1,1,1,3,3-pentafluoro-2,3-dichloropropane.
 2. An azeotropic compositionconsisting substantially of 85 to 95 mol% of hydrogen fluoride and 15 to5 mol% of 1,1,1,3,3-pentafluoro-2,3-dichloropropane having a boilingpoint in a range of 16 to 19° C. at a pressure of 1 Kg/cm² -abs.
 3. Aprocess of separating hydrogen fluoride or1,1,1,3,3-pentafluoro-2,3-dichloropropane from a mixture which compriseshydrogen fluoride and 1,1,1,3,3-pentafluoro-2,3-dichloropropane whereinthe mixture is subjected to distillation so that hydrogen fluoride and1,1,1,3,3-pentafluoro-2,3-dichloropropane are distilled off as anazeotropic composition thereof.
 4. A process of purifying1,1,1,3,3-pentafluoro-2,3-dichloropropane characterized in that anazeotropic composition containing hydrogen fluoride and1,1,1,3,3-pentafluoro-2,3-dichloropropane is liquid-separated to obtaina lower liquid phase which is rich in 1,1,1,3,3-pentafluoro-2,3-dichloropropane, which phase is subjected to adistillation step so that an azeotropic composition of hydrogen fluorideand 1,1,1,3,3-pentafluoro-2,3-dichloropropane is withdrawn from thelower liquid phase, whereby 1,1,1,3,3-pentafluoro-2,3-dichloropropane isobtained which is substantially free of hydrogen fluoride.
 5. Theprocess of claim 3, wherein the azeotropic composition consistsessentially of 85 to 95 mol% of hydrogen fluoride and 15 to 5 mol% of1,1,1,3,3-pentafluoro-2,3-dichloropropane.
 6. The process of claim 4wherein the azeotropic composition consists essentially of 85 to 95 mol%of hydrogen fluoride and 15 to 5 mol% of1,1,1,3,3-pentafluoro-2,3-dichloropropane.
 7. The process of claim 5,wherein the azeotropic composition has a boiling point in a range of 16to 19° C. at a pressure of Kg/cm² -abs.
 8. The process of claim 5,wherein the azeotropic composition has a boiling point in a range of 16to 19° C. at a pressure of Kg/cm² -abs.